Determining whether fluid is flowing through a hard-walled opaque pipe can be important for a number of reasons. In the plant setting, a failure to make the correct determination can result in waste and/or destruction on a massive scale, personal injury, and death.
A device which enables one to visually ascertain from a distance whether fluid is flowing within pipe is described in my U.S. Pat. No. 6,526,907, issued Mar. 4, 2003. The disclosure of this patent is incorporated by reference herein. The patent discloses a flow indicating device which is highly visible, easy to read, and is viewable from any location around the pipe.
While this device is a noteworthy advance in the art, it has been possible to improve it in several areas, primarily from the standpoints of providing a lower pressure drop, less turbulence, greater ease of manufacturing, and improved performance particularly at low flow rates.